Generally, glass plates are widely used as the substrates for displays such as liquid crystal and organic EL displays. However, glass plates have a large specific gravity and are difficult to reduce in weight, and also suffer from other drawbacks such as being susceptible to breakage, unable to bend, and requiring a predetermined thickness. As a result, in recent years, plastic substrates that can replace glass plates are being investigated. Specifically, display substrates using polycarbonate, polyethylene naphthalate or polyethylene terephthalate are now being used.
However, these conventional plastic materials for replacing glass have a large coefficient of linear expansion compared with a glass plate, and therefore during the process of depositing a device layer such as a thin film transistor on the substrate at high temperature, problems such as warping, cracking of the deposited film, and semiconductor disconnection tend to occur readily, meaning practical application of such plastic materials has proven difficult.
In other words, for these applications, a plastic material having high transparency, high heat resistance, low water absorption and a low coefficient of linear expansion is required.
In recent years, materials that use cellulose have been proposed as materials having these types of properties. Specifically, Patent Document 1 discloses that a composite composed of a nonwoven fabric containing cellulose and a resin other than cellulose exhibits excellent heat resistance, transparency and coefficient of linear expansion. Further, Patent Document 2 discloses a fiber composite, which contains cellulose fibers having an average fiber diameter of not more than 30 nm and a matrix material, and displays prescribed optical properties, and it can be anticipated that by using cellulose fibers having an ultra fine fiber diameter at the nanometer level, composites having even superior performance should be obtainable.
On the other hand, in these documents, the method used for obtaining the composite uses a technique in which, first, a dispersion containing the cellulose is filtered (papermaking) to produce a nonwoven fabric composed of cellulose, and the nonwoven fabric is subsequently complexed with another material.